Gases, pressure and temperature Cambridge IGCSE Physics (9–1) revision
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In plain words
Trap some gas and you can change three things: its pressure, its volume and its temperature. Squash it into a smaller volume and the pressure goes up. Heat it in a fixed container and the pressure goes up. At a steady temperature, pressure × volume stays the same.
Three things to know
- Heating a gas in a fixed volume increases its pressure: the particles move faster and hit the walls harder and more often.
- At constant temperature, pressure × volume is constant for a fixed mass of gas (p₁V₁ = p₂V₂). Halve the volume and the pressure doubles.
- Kelvin temperature = Celsius temperature + 273. Absolute zero (0 K, −273 °C) is where particles have their least possible energy.
Worked example
A gas has a volume of 60 cm³ at a pressure of 100 kPa. It is squashed to 20 cm³ at the same temperature. Find the new pressure.
- p₁V₁ = p₂V₂, so 100 × 60 = p₂ × 20.
- p₂ = 6000 ÷ 20.
- = 300 kPa.
Tips and tricks
- Sense-check: a smaller volume must give a bigger pressure. If your answer went the other way, you divided by the wrong number.
- To change °C into kelvin, add 273.
It lands in your notebook with its questions as flashcards.
Gases, pressure and temperature: 6 questions and answers
These are the quiz’s questions. Do the quiz first, then come back here for the ones that got you.
What is 0 °C in kelvin?
Add 273 to the Celsius temperature.
The volume of a fixed mass of gas is halved at constant temperature. What happens to the pressure?
Pressure × volume stays constant.
What is absolute zero?
It is the lowest possible temperature, 0 K.
A sealed can of gas is heated. Why does the pressure rise?
Faster particles collide with more force and more frequently.
A gas at 200 kPa has a volume of 3 m³. At the same temperature its volume becomes 6 m³. What is the pressure?
200 × 3 = p × 6, so p = 100 kPa.
What is 400 K in degrees Celsius?
Subtract 273.
Quiz
6 questions
Tap an answer and you’ll see straight away whether it’s right, and why.
Worksheet
4 questions, 10 marks. Write your answers on paper, then check them.
Gases, pressure and temperature
Cambridge IGCSE Physics (9–1) 0972 · 10 marks · papermunch.org
Name ______________________________ Date ______________
Convert 27 °C to kelvin.[1]
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300 K. 27 + 273.
A gas has a volume of 600 cm³ at a pressure of 100 kPa. It is compressed at constant temperature to 200 cm³. Calculate the new pressure.[3]
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300 kPa. 100 × 600 = p × 200.
Explain, using ideas about particles, why the pressure in a car tyre rises on a hot day.[3]
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The air particles move faster, so they hit the tyre walls harder and more often.
A gas at 150 kPa occupies 4.0 m³. It expands at constant temperature until its pressure is 50 kPa. Calculate its new volume.[3]
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12 m³. 150 × 4.0 = 50 × V.
Answers: Gases, pressure and temperature
- 1. 300 K. 27 + 273.
- 2. 300 kPa. 100 × 600 = p × 200.
- 3. The air particles move faster, so they hit the tyre walls harder and more often.
- 4. 12 m³. 150 × 4.0 = 50 × V.